Refrigeration oil, and composition for use in refrigerating machine

ABSTRACT

A refrigerator oil according to one embodiment of the present invention contains: a base oil containing an oxygen-containing organic compound; a polyphosphate ester compound; and a metal salt of an organic carboxylic acid having 6 to 60 carbon atoms.

TECHNICAL FIELD

The present invention relates to a refrigerator oil, and a composition for a refrigerator using the refrigerator oil.

BACKGROUND ART

A refrigerator has a structure, in which a mixture of a refrigerant and a refrigerator oil (which may be hereinafter referred to as a “composition for a refrigerator”) is circulated in a closed system, and the refrigerator oil is demanded to have compatibility with a refrigerant, stability, and lubricating capability. For facilitating the satisfaction of these demanded capabilities, a refrigerator oil containing an oxygen-containing organic compound, such as a vinyl ether compound, as a major component has been frequently used (see, for example, PTL 1).

A refrigerant used in recent years is becoming a hydrofluorocarbon (HFC) instead of a hydrochlorofluorocarbon (HCFC) having a high environmental load. In the HFC, a saturated hydrofluorocarbon (saturated HFC), such as R32 (difluoroethane) and R410A (a mixture of difluoroethane and pentafluoroethane), is frequently used.

As a technique for improving the compatibility with the saturated HFC refrigerant and the lubricating capability, such as the wear resistance and the seize resistance, it has been known that a phosphate ester compound having one phosphorus atom, such as tricresyl phosphate (TCP), is added to a base oil containing an oxygen-containing organic compound (see, for example, PTL 2).

For example, furthermore, PTLs 3 to 5 describe that a fatty acid alkali metal salt is blended with a refrigerator oil for the purpose of enhancing the wear resistance and the like. Moreover, PTL 3 to 5 describe that a phosphate ester compound having one phosphorus atom, such as TCP, is blended in addition to the fatty acid alkali metal salt.

CITATION LIST Patent Literatures

PTL 1: JP 6-128578 A

PTL 2: JP 10-130683 A

PTL 3: JP 2001-3072 A

PTL 4: JP 4-300996 A

PTL 5: WO 2008/041549

SUMMARY OF INVENTION Technical Problem

There is an increasing demand of energy saving for various refrigerators in recent years, and the enhancement of the coefficient of performance (COP) is being demanded. Accordingly, the refrigerator oil is demanded to achieve a lower coefficient of friction in a sliding portion in a refrigerator for the enhancement of the COP, in addition to the wear resistance.

However, as shown in PTLs 2 to 5, the lubricating oil composition is difficult to decrease the coefficient of friction sufficiently while improving the wear resistance in a sliding portion of a refrigerator, by blending therewith a phosphate ester compound having one phosphorus atom, such as TCP, a fatty acid alkali metal salt, or both of them.

The present invention has been made in view of the aforementioned problem, and an object thereof is to decrease the coefficient of friction while improving the wear resistance in the case where a refrigerator oil containing an oxygen-containing organic compound as a base oil is used.

Solution to Problem

As a result of earnest investigations, the present inventors have found that the problem can be solved by adding both a particular phosphorus compound having two or more phosphorus atoms in one molecule and an organic carboxylic acid metal salt to a base oil containing an oxygen-containing organic compound, and thus the present invention has been completed. The present invention provides the refrigerator oil, the composition for a refrigerator, and a method for producing a refrigerator oil shown below.

(1) A refrigerator oil containing: a base oil containing an oxygen-containing organic compound; a polyphosphate ester compound; and a metal salt of an organic carboxylic acid having 6 to 60 carbon atoms.

(2) A composition for a refrigerator, containing: a refrigerant and the refrigerator oil according to the item (1).

(3) A method for producing a refrigerator oil, including blending at least a polyphosphate ester compound and a metal salt of an organic carboxylic acid having 6 to 60 carbon atoms with a base oil containing an oxygen-containing organic compound to obtain a refrigerator oil.

Advantageous Effects of Invention

According to the present invention, both a particular phosphorus compound and a metal salt of an organic carboxylic acid are added to a base oil, thereby providing a refrigerator oil that is capable of decreasing the coefficient of friction while improving the wear resistance.

DESCRIPTION OF EMBODIMENTS

The present invention will be described with reference to embodiments below.

The refrigerator oil according to one embodiment of the present invention contains a base oil, a polyphosphate ester compound, and a metal salt of an organic carboxylic acid. The components contained in the refrigerator oil will be described in detail below.

[Base Oil]

The base oil in the present embodiment contains an oxygen-containing organic compound. Examples of the oxygen-containing organic compound include a synthetic oil containing an ether group, a ketone group, an ester group, a carbonate group, or the like in the molecule, and a synthetic oil containing these groups and a hetero atom (such as a sulfur atom, a fluorine atom, a chlorine atom, a silicon atom, and a nitrogen atom). More specifically, examples thereof include a polyvinyl ether compound (PVE), a polyoxyalkylene glycol compound (PAG), a copolymer of a poly(oxy)alkylene glycol or a monoether thereof and a polyvinyl ether (ECP), and a polyol ester compound (POE). The oxygen-containing organic compound may be used solely or as a combination of two or more kinds thereof.

Among these, one or more selected from a polyvinyl ether compound (PVE) and a polyoxyalkylene glycol compound (PAG) is preferred, and in particular, one or more selected from a polyvinyl ether compound (PVE) is more preferred. The coefficient of friction and the wear resistance can be readily improved in the case where PVE is used with a polyphosphate ester compound represented by the general formula (1), in which R⁹ represents a group represented by the general formula (2), or a polyphosphate ester compound represented by the general formula (5), which are described later.

The oxygen-containing organic compound is a major component of the refrigerator oil, and the oxygen-containing organic compound is preferably contained in an amount of from 70 to 99.98% by mass, more preferably from 90 to 99.5% by mass, and further preferably from 93.0 to 99.3% by mass, based on the total amount of the refrigerator oil.

PVE, PAG, ECP, and POE used as the base oil will be described in more detail below.

<Polyvinyl Ether Compound (PVE)>

The polyvinyl ether compound (PVE) is a polymer having a constituent unit derived from a vinyl ether, and specifically, examples thereof include a polyvinyl compound having a constituent unit represented by the following general formula (A-1).

In the general formula (A-1), R^(1a), R^(2a), and R^(3a) each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other. Specific examples of the hydrocarbon group include an alkyl group, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, and octyl groups of every kind; a cycloalkyl group, such as a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups of every kind, ethylcyclohexyl groups of every kind, and dimethylcyclohexyl groups of every kind; an aryl group, such as a phenyl group, methylphenyl groups of every kind, ethylphenyl groups of every kind, and dimethylphenyl groups of every kind; and an arylalkyl group, such as a benzyl group, phenylethyl groups of every kind, and methylbenzyl groups of every kind. Among those, an alkyl group is preferred.

R^(1a), R^(2a), and R^(3a) each are more preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, and it is further preferred that all of them are hydrogen atoms. r in the general formula (A-1) represents a repetition number, an average value of which is in a range of from 0 to 10, and is more preferably 0.

R^(4a) represents a divalent hydrocarbon group having 2 to 10 carbon atoms. Specific examples of the divalent hydrocarbon group having 2 to 10 carbon atoms include a divalent aliphatic hydrocarbon group, such as an ethylene group, a phenylethylene group, a 1,2-propylene group, a 2-phenyl-1,2-propylene group, a 1,3-propylene group, butylene groups of every kind, pentylene groups of every kind, hexylene groups of every kind, heptylene groups of every kind, octylene groups of every kind, nonylene groups of every kind, and decylene groups of every kind; an alicyclic hydrocarbon group having two bonding sites in an alicyclic hydrocarbon, such as cyclohexane, methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, and propylcyclohexane; a divalent aromatic hydrocarbon group, such as phenylene groups of every kind, methylphenylene groups of every kind, ethylphenylene groups of every kind, dimethylphenylene groups of every kind, and naphthylene groups of every kind; an alkyl aromatic hydrocarbon group having a monovalent bonding site in each of an alkyl group moiety and an aromatic moiety of an alkyl aromatic hydrocarbon such as toluene and ethylbenzene; and an alkyl aromatic hydrocarbon group having bonding sites in an alkyl group moiety of a polyalkyl aromatic hydrocarbon, such as xylene and diethylbenzene. Among those, the aliphatic hydrocarbon group having 2 to 4 carbon atoms is more preferred. The plural groups represented by R^(4a)O may be the same as or different from each other.

Furthermore, in the general formula (A-1), R^(5a) represents a hydrocarbon group having 1 to 10 carbon atoms. Specific examples of the hydrocarbon group include an alkyl group, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, octyl groups of every kind, nonyl groups of every kind, and decyl groups of every kind; a cycloalkyl group, such as a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups of every kind, ethylcyclohexyl groups of every kind, propylcyclohexyl groups of every kind, and dimethylcyclohexyl groups of every kind; an aryl group, such as a phenyl group, methylphenyl groups of every kind, ethylphenyl groups of every kind, dimethylphenyl groups of every kind, propylphenyl groups of every kind, trimethylphenyl groups of every kind, butylphenyl groups of every kind, and naphthyl groups of every kind; or an arylalkyl group, such as a benzyl group, phenylethyl groups of every kind, methylbenzyl groups of every kind, phenylpropyl groups of every kind, and phenylbutyl groups of every kind. Among those, a hydrocarbon group having 1 to 8 carbon atoms is preferred, and an alkyl group having 1 to 6 carbon atoms is more preferred. The alkyl groups may be any of straight-chain, branched, and cyclic groups.

In the polyvinyl compound having the constituent unit represented by the general formula (A-1), a polymer or a copolymer containing from 50 to 100% by mol of a constituent unit, in which R^(1a), R^(2a), and R^(3a) are all hydrogen atoms, r is 0, and R^(5a) is an ethyl group, and containing from 0 to 50% by mol of a constituent unit, in which R^(1a), R^(2a), and R^(3a) are all hydrogen atoms, r is 0, and R^(5a) is an alkyl group having 3 or 4 carbon atoms, is preferred. It is more preferred that the proportion of the constituent unit, in which R^(5a) is an ethyl group, is from 70 to 100% by mol, and the proportion of the constituent unit, in which R^(5a) is an alkyl group having 3 or 4 carbon atoms, is from 0 to 30% by mol, and it is further preferred that the proportion of the former is from 80 to 95%, and the proportion of the latter is from 5 to 20% by mol.

The alkyl group having 3 or 4 carbon atoms in R^(5a) used may be a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, or a tert-butyl group, and an isobutyl group is particularly preferred.

While the polyvinyl ether compound has the constituent unit represented by the general formula (A-1), a repeating number thereof may be appropriately selected according to a desired kinematic viscosity. The polyvinyl ether compound can be produced through polymerization of a corresponding vinyl ethereal monomer. The vinyl ethereal monomer that can be used herein is represented by the following general formula (A-2).

In the formula (A-2), R^(1a), R^(2a), R^(3a), R^(4a), R^(5a), and r have the same meanings as above.

As the vinyl ethereal monomer, there are various monomers corresponding to the aforementioned polyvinyl ether compounds. Examples thereof include vinyl methyl ether, vinyl ethyl ether, vinyl-n-propyl ether, vinyl-isopropyl ether, vinyl-n-butyl ether, vinyl-isobutyl ether, vinyl-sec-butyl ether, vinyl-tert-butyl ether, vinyl-n-pentyl ether, vinyl-n-hexyl ether, vinyl-2-methoxyethyl ether, vinyl-2-ethoxyethyl ether, vinyl-2-methoxy-1-methylethyl ether, vinyl-2-methoxypropyl ether, vinyl-3,6-dioxaheptyl ether, vinyl-3,6,9-trioxadecyl ether, vinyl-1,4-dimethyl-3,6-dioxaheptyl ether, vinyl-1,4,7-trimethyl-3,6,9-trioxadecyl ether, vinyl-2,6-dioxa-4-heptyl ether, vinyl-2,6,9-trioxa-4-decyl ether, 1-methoxypropene, 1-ethoxypropene, 1-n-propoxypropene, 1-isopropoxypropene, 1-n-butoxypropene, 1-isobutoxypropene, 1-sec-butoxypropene, 1-tert-butoxypropene, 2-methoxypropene, 2-ethoxypropene, 2-n-propoxypropene, 2-isopropoxypropene, 2-n-butoxypropene, 2-isobutoxypropene, 2-sec-butoxypropene, 2-tert-butoxypropene, 1-methoxy-1-butene, 1-ethoxy-1-butene, 1-n-propoxy-1-butene, 1-isopropoxy-1-butene, 1-n-butoxy-1-butene, 1-isobutoxy-1-butene, 1-sec-butoxy-1-butene, 1-tert-butoxy-1-butene, 2-methoxy-1-butene, 2-ethoxy-1-butene, 2-n-propoxy-1-butene, 2-isopropoxy-1-butene, 2-n-butoxy-1-butene, 2-isobutoxy-1-butene, 2-sec-butoxy-1-butene, 2-tert-butoxy-1-butene, 2-methoxy-2-butene, 2-ethoxy-2-butene, 2-n-propoxy-2-butene, 2-isopropoxy-2-butene, 2-n-butoxy-2-butene, 2-isobutoxy-2-butene, 2-sec-butoxy-2-butene, and 2-tert-butoxy-2-butene. These vinyl ethereal monomers can be produced by a known method.

In an end moiety of the polymer represented by the general formula (A-1), a monovalent group derived from a saturated hydrocarbon, an ether, an alcohol, a ketone, an amide, a nitrile, or the like may be introduced by a known method.

In particular, as the polyvinyl ether compound, compounds having an end structure of each of the following items (1) to (4) are preferred.

(1) A compound, in which one end thereof is represented by the following general formula (A-1-i), and the remaining end is represented by the following general formula (A-1-ii)

In the formula, R^(6a), R^(7a), and R^(8a) each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other; R^(9a) represents a divalent hydrocarbon group having 2 to 10 carbon atoms; R^(10a) represents a hydrocarbon group having 1 to 10 carbon atoms; r1 represents a number of from 0 to 10 in terms of average value thereof; and in the case where plural groups represented by R^(9a)O are present, the plural groups represented by R^(9a)O may be the same as or different from each other.

In the formula, R^(11a), R^(12a), and R^(13a) each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other; R^(14a) represents a divalent hydrocarbon group having 2 to 10 carbon atoms; R^(15a) represents a hydrocarbon group having 1 to 10 carbon atoms; r2 represents a number of from 0 to 10 in terms of average value thereof; and in the case where plural groups represented by R^(14a)O are present, the plural groups represented by R^(14a)O may be the same as or different from each other.

(2) A compound, in which one end thereof is represented by the foregoing general formula (A-1-i), and the remaining end is represented by the following general formula (A-1-iii)

In the formula, R^(16a), R^(17a), and R^(18a) each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other; R^(19a) and R^(21a) each independently represent a divalent hydrocarbon group having 2 to 10 carbon atoms, and may be the same as or different from each other; R^(20a) and R^(22a) each independently represent a hydrocarbon group having 1 to 10 carbon atoms, and may be the same as or different from each other; r3 and r4 each represent a number of from 0 to 10 in terms of average value thereof, and may be the same as or different from each other; in the case where plural groups represented by R^(19a)O are present, the plural groups represented by R^(19a)O may be the same as or different from each other; and in the case where plural groups represented by R^(21a)O are present, the plural groups represented by R^(21a)O may be the same as or different from each other.

(3) A compound, in which one end thereof is represented by the foregoing general formula (A-1-i), and the remaining end has an olefinic unsaturated bond

(4) A compound, in which one end thereof is represented by the foregoing general formula (A-1-i), and the remaining end is represented by the following general formula (A-1-iv)

In the formula, R^(23a), R^(24a), and R^(25a) each represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other.

The polyvinyl ether compound may also be a mixture of two or more selected from those having an end structure of each of the items (1) to (4). Preferred examples of the mixture include a mixture of the compound having the end structure of the item (1) and the compound having the end structure of the item (4); and a mixture of the compound having the end structure of the item (2) and the compound having the end structure of the item (3).

As for the polyvinyl ether compound, it is preferred to select a degree of polymerization, an end structure, and the like, so as to have a preferred viscosity range of the base oil described later. The polyvinyl ether compound may be used solely or may be used as a combination of two or more kinds thereof.

In the polyvinyl compound having the constituent unit represented by the general formula (A-1), a compound, in which one end thereof is presented by the general formula (A-1-i), and the remaining end is represented by the general formula (A-1-ii) is preferred.

Among these, it is more preferred that in the formulae (A-1-i) and (A-1-ii), all of R^(6a), R^(7a), R^(8a), R^(11a), R^(12a), and R^(13a) are hydrogen atoms, all of r1 and r2 are 0, and R^(10a) and R^(15a) are each an alkyl group having 1 to 4 carbon atoms.

<Polyoxyalkylene Glycol Compound (PAG)>

Examples of the polyoxyalkylene glycol compound (PAG) include a compound represented by the following general formula (B-1). In the case where PAG is contained in the base oil, the PAG may be used either solely or as a combination of two or more kinds thereof.

R^(1b)—[(OR^(2b))_(m)—OR^(3b)]_(n)  (B-1)

In the formula, R^(1b) represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, a hydrocarbon group having 2 to 6 bonding sites and having 1 to 10 carbon atoms, or an oxygen-containing hydrocarbon group having 1 to 10 carbon atoms; R^(2b) represents an alkylene group having 2 to 4 carbon atoms; R^(3b) represents a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or an oxygen-containing hydrocarbon group having 1 to 10 carbon atoms; n represents an integer of 1 to 6; and m represents a number providing of an average value of m×n of from 6 to 80.

In the general formula (B-1), the monovalent hydrocarbon group having 1 to 10 carbon atoms in each of R^(1b) and R^(3b) may be any of straight-chain, branched, and cyclic groups. The hydrocarbon group is preferably an alkyl group, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, butyl groups of every kind, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, octyl groups of every kind, nonyl groups of every kind, decyl groups of every kind, a cyclopentyl group, and a cyclohexyl group. As for the aforementioned monovalent hydrocarbon group, when the number of carbon atoms is 10 or less, the compatibility with a refrigerant becomes good. From such a viewpoint, the number of carbon atoms of the monovalent hydrocarbon group is more preferably from 1 to 4.

The hydrocarbon group moiety which the acyl group having 2 to 10 carbon atoms in each of R^(1b) and R^(3b) has may be any of straight-chain, branched, and cyclic groups. The hydrocarbon group moiety of the acyl group is preferably an alkyl group, and specific examples thereof include those having 1 to 9 carbon atoms among the alkyl groups that may be selected as the aforementioned R^(1b) and R^(3b). When the number of carbon atoms of the acyl group is 10 or less, the compatibility with a refrigerant becomes good. The number of carbon atoms of the acyl group is preferably from 2 to 4.

In the case where all of R^(1b) and R^(3b) are a hydrocarbon group or an acyl group, R^(1b) and R^(3b) may be the same as or different from each other.

In the case where n is 2 or more, plural groups represented by R^(3b) in one molecule may be the same as or different from each other.

In the case where R^(1b) is the hydrocarbon group having 2 to 6 bonding sites and having 1 to 10 carbon atoms, the hydrocarbon group may be either linear or cyclic. The hydrocarbon group having 2 bonding sites is preferably an aliphatic hydrocarbon group, and examples thereof include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, a cyclopentylene group, and a cyclohexylene group. Examples of the other hydrocarbon groups include residues resulting from removing a hydroxyl group from a bisphenol compound such as bisphenol, bisphenol F, and bisphenol A. The hydrocarbon group having 3 to 6 bonding sites is preferably an aliphatic hydrocarbon group, and examples thereof include residues resulting from removing a hydroxyl group from a polyhydric alcohol, such as trimethylolpropane, glycerin, pentaerythritol, sorbitol, 1,2,3-trihydroxycyclohexane, and 1,3,5-trihydroxycyclohexane.

When the number of carbon atoms of the aliphatic hydrocarbon group is 10 or less, the compatibility with a refrigerant becomes good. The number of carbon atoms of the aliphatic hydrocarbon group is preferably from 2 to 6.

Examples of the oxygen-containing hydrocarbon group having 1 to 10 carbon atoms in each of R^(1b) and R^(3b) include an ether bond-containing linear or cyclic aliphatic group (for example, a tetrahydrofurfuryl group).

At least one of R^(1b) and R^(3b) is preferably an alkyl group, particularly preferably an alkyl group having 1 to 4 carbon atoms.

R^(2b) in the general formula (B-1) is an alkylene group having 2 to 4 carbon atoms, and examples of the oxyalkylene group as a repeating unit include an oxyethylene group, an oxypropylene group, and an oxybutylene group. The oxyalkylene groups in one molecule may be the same as each other, and two or more kinds of oxyalkylene groups may also be contained. It is preferred that at least an oxypropylene unit is contained in one molecule, and it is more preferred that 50% by mol or more of an oxypropylene unit is contained in the oxyalkylene unit.

In the general formula (B-1), n is an integer of from 1 to 6 and is determined according to the number of bonding sites of R^(1b). For example, in the case where R^(1b) is an alkyl group or an acyl group, then n is 1; and in the case where R^(1b) is an aliphatic hydrocarbon group having 2, 3, 4, 5, or 6 bonding sites, then n is 2, 3, 4, 5, or 6, respectively. m is a number providing an average value of m×n of from 6 to 80. When the average value is 80 or less, the compatibility with a refrigerant may be improved. n is preferably an integer of from 1 to 3, and more preferably 1. The average value of m×n is preferably determined in such a manner that the viscosity of the base oil is in the desired range described later. The polyoxyalkylene glycol compound represented by the general formula (B-1) encompasses a polyoxyalkylene glycol having a hydroxyl group at the end thereof, which may be preferably used even though a hydroxyl group is contained when the content of the hydroxyl group is 50% by mol or less based on the whole end groups.

<Copolymer of Poly(Oxy)Alkylene Glycol or Monoether Thereof and Polyvinyl Ether (ECP)>

In the refrigerator oil according to the present embodiment, examples of the copolymer of a poly(oxy)alkylene glycol or a monoether thereof and polyvinyl ether that can be used as the base oil include a copolymer represented by the following general formula (C-1) and a copolymer represented by the following general formula (C-2) (hereinafter referred to as a “polyvinyl ether copolymer I” and a “polyvinyl ether copolymer II”, respectively). The poly(oxy)alkylene glycol refers to both a polyalkylene glycol and a polyoxyalkylene glycol.

In the general formula (C-1), R^(1c), R^(2c), and R^(3c) each independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and may be the same as or different from each other; R^(5c) represents a divalent hydrocarbon group having 2 to 4 carbon atoms; R^(6c) represents an aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 1 to 20 carbon atoms, an acyl group having 2 to 20 carbon atoms, or an oxygen-containing hydrocarbon group having 2 to 50 carbon atoms; R^(4c) represents a hydrocarbon group having 1 to 10 carbon atoms; and in the case where plural groups represented by each of R^(1c) to R^(6c) are present, the groups may be each the same as or different from each other.

Specific examples of the hydrocarbon group having 1 to 8 carbon atoms in R^(1c) to R^(3c) include an alkyl group, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, and octyl groups of every kind; a cycloalkyl group, such as a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups of every kind, ethylcyclohexyl groups of every kind, and dimethylcyclohexyl groups of every kind; an aryl group, such as dimethylphenyl groups of every kind; or an arylalkyl group, such as a benzyl group, phenylethyl groups of every kind, and methylbenzyl groups of every kind. In particular, R^(1c), R^(2c), and R^(3c) are each preferably a hydrogen atom.

Specific examples of the divalent hydrocarbon group having 2 to 4 carbon atoms represented by R^(5e) include a divalent alkylene group, such as a methylene group, an ethylene group, propylene groups of every kind, and butylene group of every kind.

In the general formula (C-1), v represents a repeating number of R^(5c)O, and is a number providing an average value thereof of from 1 to 50, preferably from 1 to 20, more preferably from 1 to 10, and further preferably from 1 to 5. In the case where plural groups represented by R^(5c)O are present, the plural groups represented by R^(5c)O may be the same as or different from each other. v may be the same as or different from each other in every constituent unit.

w represents a number of from 1 to 50, preferably from 1 to 10, more preferably from 1 to 2, and further preferably 1; u represents a number of from 0 to 50, preferably from 2 to 25, and more preferably from 6 to 15; and in the case where plural numbers represented by each of w and u are present, the numbers may provide either a block form or a random form.

In the general formula (C-1), R^(6c) preferably represents an alkyl group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or an oxygen-containing hydrocarbon group having 2 to 50 carbon atoms.

Specific examples of the alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, octyl groups of every kind, nonyl groups of every kind, decyl groups of every kind, a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups of every kind, ethylcyclohexyl groups of every kind, propylcyclohexyl groups of every kind, and dimethylcyclohexyl groups of every kind.

Examples of the acyl group having 2 to 10 carbon atoms include an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a valeryl group, an isovaleryl group, a pivaloyl group, a benzoyl group, and a toluoyl group.

Preferred examples the oxygen-containing hydrocarbon group having 2 to 50 carbon atoms include a methoxymethyl group, a methoxyethyl group, a methoxypropyl group, a 1,1-bismethoxypropyl group, a 1,2-bismethoxypropyl group, an ethoxypropyl group, a (2-methoxyethoxy)propyl group, and a (1-methyl-2-methoxy)propyl group.

In the general formula (C-1), specific examples of the hydrocarbon group having 1 to 10 carbon atoms represented by R^(4c) include an alkyl group, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, octyl groups of every kind, nonyl groups of every kind, and decyl groups of every kind; a cycloalkyl group, such as a cyclopentyl group, a cyclohexyl group, methylcyclohexyl groups of every kind, ethylcyclohexyl groups of every kind, propylcyclohexyl groups of every kind, and dimethylcyclohexyl groups of every kind; an aryl group, such as a phenyl group, methylphenyl groups of every kind, ethylphenyl groups of every kind, dimethylphenyl groups of every kind, propylphenyl groups of every kind, trimethylphenyl groups of every kind, butylphenyl groups of every kind, and naphthyl groups of every kind; and an arylalkyl group, such as a benzyl group, phenylethyl groups of every kind, methylbenzyl groups of every kind, phenylpropyl groups of every kind, and phenylbutyl groups of every kind.

The polyvinyl ether copolymer I having the constituent unit represented by the general formula (C-1) is capable of improving the lubricating properties, the insulating properties, the hygroscopicity, and the like, while satisfying the compatibility, through formation of the copolymer.

In the polyvinyl ether copolymer II represented by the general formula (C-2), R^(1c) to R^(5c) and v are the same as those mentioned above. In the case where plural groups represented by each of R^(4c) and R^(5c) are present, the groups may be each the same as or different from each other. x and y each represent a number of from 1 to 50, and in the case where plural numbers represented by each of x and y are present, the numbers may provide either a block form or a random form. X^(c) and Y^(c) each independently represent a hydrogen atom, a hydroxyl group, or a hydrocarbon group having 1 to 20 carbon atoms.

It is preferred that the repeating numbers u, w, x, and y in the general formulae (C-1) and (C-2) are properly selected in such a manner that a desired viscosity described later is obtained. The production method of each of the polyvinyl ether copolymers I and II is not particularly limited, as far as the method can provide the polyvinyl ether copolymers I and II.

The vinyl ethereal copolymer I represented by the general formula (C-1) can be formed into a polyvinyl ether copolymer I having a structure, in which one end thereof is represented by the following general formula (C-3) or (C-4), and the remaining end is represented by the following general formula (C-5) or (C-6).

In the aforementioned (C-3) and (C-4), R^(1c) to R^(6c) and v are the same as those as mentioned above.

In the aforementioned (C-5) and (C-6), R^(1c) to R^(6c) and v are the same as those as mentioned above.

<Polyol Ester Compound (POE)>

In the refrigerator oil, as the polyol ester compound that can be used as the base oil, an ester of a diol or a polyol having 3 to 20 hydroxyl groups and a fatty acid having 1 to 24 carbon atoms is preferably used. Examples of the diol include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol. Examples of the polyol include a polyhydric alcohol, such as trimethylolethane, trimethylolpropane, trimethylolbutane, di(trimethylolpropane), tri(trimethylolpropane), pentaerythritol, di(pentaerythritol), tri(pentaerythritol), glycerin, a polyglycerin (e.g., dimer to icosamer of glycerin), 1,3,5-pentanetriol, sorbitol, sorbitan, a sorbitol glycerin condensate, adonitol, arabitol, xylitol, and mannitol; a saccharide, such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose, and merenditose; a partially etherified product thereof, and a methyl glucoside (a glucoside). Among these, hindered alcohols, such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di(trimethylolpropane), tri(trimethylolpropane), pentaerythritol, di(pentaerythritol), and tri(pentaerythritol), are preferred as the polyol.

The fatty acid used may be a fatty acid having 1 to 24 carbon atoms while the number of carbon atoms thereof is not particularly limited. In the fatty acid having 1 to 24 carbon atoms, a fatty acid having 3 or more carbon atoms is preferred, a fatty acid having 4 or more carbon atoms is more preferred, and a fatty acid having 5 or more carbon atoms is further preferred, from standpoint of the lubricating properties. A fatty acid having 18 or less carbon atoms is preferred, a fatty acid having 12 or less carbon atoms is more preferred, and a fatty acid having 9 or less carbon atoms is further preferred, from the standpoint of the compatibility with a refrigerant.

The fatty acid may be any of a straight-chain fatty acid and a branched fatty acid, a straight-chain fatty acid is preferred from the standpoint of the lubricating properties, and a branched fatty acid is preferred from the standpoint of the hydrolysis stability. Furthermore, the fatty acid may be any of a saturated fatty acid and an unsaturated fatty acid.

Examples of the fatty acid include a straight-chain or branched fatty acid, such as isobutyric acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, and icosanoic acid, oleic acid; and a so-called neo acid, in which an α-carbon atom is quaternary. More specifically, isobutyric acid, valeric acid (n-pentanoic acid), caproic acid (n-hexanoic acid), enanthic acid (n-heptanoic acid), caprylic acid (n-octanoic acid), pelargonic acid (n-nonanoic acid), capric acid (n-decanoic acid), oleic acid (cis-9-octadecenoic acid), isopentanoic acid (3-methylbutanoic acid), 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid, and the like are preferred.

The polyol ester may be a partial ester, in which some of the hydroxyl groups of a polyol remain without being esterified, may be a complete ester, in which all of the hydroxyl groups of the polyol are esterified, or may be a mixture of the partial ester and the complete ester, but the polyol ester is preferably the complete ester.

Among the polyol esters, due to the excellent hydrolysis stability, esters of a hindered alcohol, such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di(trimethylolpropane), tri(trimethylolpropane), pentaerythritol, di(pentaerythritol), and tri(pentaerythritol), are preferred, esters of neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, and pentaerythritol are more preferred, and esters of pentaerythritol are most preferred since they are particularly excellent in compatibility with a refrigerant and hydrolysis stability.

Specific examples of the preferred polyol ester include a diester of neopentyl glycol and one or more fatty acids selected from isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid; a triester of trimethylolethane and one or more fatty acids selected from isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid; a triester of trimethylolpropane and one or more fatty acids selected from isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid; a triester of trimethylolbutane and one or more fatty acids selected from isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid; and a tetraester of pentaerythritol and one or more fatty acids selected from isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid.

The ester of two or more fatty acids may be a mixture of two or more esters of one fatty acid and a polyol, and an ester of a mixed fatty acid of two or more kinds thereof and a polyol. Particularly, an ester of a mixed fatty acid and a polyol is excellent in low-temperature properties and compatibility with a refrigerant.

The oxygen-containing organic compound contained in the refrigerator oil preferably has a kinetic viscosity at 100° C. of from 1 to 30 mm²/s. When the kinetic viscosity is 1 mm²/s or more, a good lubricating capability can be exhibited, and a good sealing property can be obtained. When the kinetic viscosity is 30 mm²/s or less, a good compatibility may be obtained between a refrigerant and the refrigerator oil, and good energy saving property can be obtained. In this point of view, the kinetic viscosity at 100° C. of the oxygen-containing organic compound is more preferably from 2 to 20 mm²/s, and further preferably from 3 to 15 mm²/s.

The base oil may contain only the oxygen-containing organic compound, and may also contain a mineral oil, a synthetic oil other than the oxygen-containing organic compound, or both of them, in addition to the oxygen-containing organic compound, unless the object of the present invention is impaired. The amount of the base oil other than the oxygen-containing organic compound is preferably less than 10% by mass, more preferably less than 5% by mass, and further preferably less than 1% by mass, based on the total amount of the refrigerator oil. The base oil other than the oxygen-containing organic compound preferably has a kinetic viscosity at 100° C. of from 1 to 30 mm²/s, more preferably from 2 to 20 mm²/s, and further preferably from 3 to 15 mm²/s, as similar to the oxygen-containing organic compound.

[Polyphosphate Ester Compound]

The polyphosphate ester compound contained in the refrigerator oil according to the present embodiment is a phosphate ester compound having at least two phosphoric acid skeletons in one molecule. Specific examples of the polyphosphate ester compound include a compound represented by the following general formula (1).

In the general formula (1), n represents an integer of from 1 to 10; R¹ to R⁸ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; and R⁹ represents a divalent hydrocarbon group having 2 to 20 carbon atoms.

The refrigerator oil according to the present embodiment can decrease the coefficient of friction and can improve the wear resistance, in a sliding portion of a refrigerator, by containing the aforementioned polyphosphate ester compound and the organic carboxylic acid metal salt described later.

The polyphosphate ester compound may be used solely or as a combination of two or more kinds thereof.

In the general formula (1), the alkyl group in R¹ to R⁸ each may be any of straight-chain, branched, and cyclic groups, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, butyl groups of every kind, pentyl groups of every kind, hexyl groups of every kind, heptyl groups of every kind, octyl groups of every kind, nonyl groups of every kind, decyl groups of every kind, undecyl groups of every kind, dodecyl groups of every kind, tridecyl groups of every kind, tetradecyl groups of every kind, pentadecyl groups of every kind, hexadecyl groups of every kind, heptadecyl groups of every kind, and octadecyl groups of every kind.

R¹ to R⁸ each preferably represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom or a methyl group, and most preferably a hydrogen atom.

In the general formula (1), R⁹ preferably represents an alkylene group, an arylene group, or a hydrocarbon group containing an alkylene group and an arylene group, and preferably contains an arylene group. In the case where R⁹ is an alkylene group, examples of the alkylene group include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tetradecylene group, a hexadecylene group, an octadecylene group, and an icosalene group, which each may be a straight-chain group, or may be branched groups of every kind. The alkylene group may also be a cyclic alkylene group, such as a cyclopropylene group, a cyclobutylene group, a cyclopentylene group, a cyclohexylene group, a cycloheptylene group, a cyclooctylene group, a dicyclopentylene group, and a tricyclopentylene group.

The arylene group may be a substituted or unsubstituted group, examples thereof include a substituted or unsubstituted phenylene group, a substituted or unsubstituted naphthylene group, and a substituted or unsubstituted biphenyl group, and the arylene group is preferably unsubstituted. Among these, a phenylene group is preferred.

In the case where R⁹ contains an arylene group and an alkylene group, the arylene group may be the same as those described above, and examples of the alkylene group include a straight-chain, branched, or cyclic alkylene group having 1 to 14 carbon atoms, and a methylene group and the groups described above can be used therefor. The alkylene group is preferably a straight-chain or branched alkylene group having 1 to 5 carbon atoms, specific examples thereof include a methylene group, ethylene groups of every kind, such as 1,1-ethylene and 1,2-ethylene, propylene groups of every kind, such as 1,3-propylene, 1,2-propylene, and 2,2-propylene, butylene groups of every kind, and pentylene groups of every kind, and among these a 2,2-propylene group (—C(CH₃)₂—) is more preferred.

In the general formula (1), n is preferably from 1 to 8, and the compound may be a single compound having only one kind of n, or may be a mixture of compounds having two or more kinds of n. n is more preferably from 1 to 3, and n is particularly preferably 1. With a smaller value of n, a smaller molecular weight is obtained, which can readily increase the solubility to the base oil, and furthermore can readily decrease the coefficient of friction.

Specific preferred examples of the group represented by R⁹ include groups represented by the following general formulae (2) to (4), and the group is more preferably a group represented by the general formula (2) or (3), and further preferably a group represented by the general formula (2). The group represented by the general formula (2) may be any of an ortho-group, a meta-group, and a para-group, and is preferably a meta-group.

Specific examples of the preferred polyphosphate ester compound include compounds represented by the following general formulae (5) and (6). Among these, a compound represented by the general formula (5) is preferred.

In the formula (5), n represents an integer of from 1 to 10, preferably from 1 to 8, and more preferably from 1 to 5. The polyphosphate ester compound represented by the general formula (5) readily exhibits the effect of improving the wear resistance and decreasing the coefficient of friction in the case where the base oil contains PVE as the oxygen-containing organic compound, and readily exhibits the effect in the case where n is from 1 to 3, and particularly in the case where n is 1.

The content of the polyphosphate ester compound is preferably from 0.01 to 5.0% by mass based on the total amount of the refrigerator oil. In the present embodiment, by adding the polyphosphate ester compound in an amount of 0.01% by mass or more, the coefficient of friction in a sliding portion can be effectively decreased while retaining the good stability and the good wear resistance of the refrigerator oil. With the content thereof of 5.0% by mass or less, the polyphosphate ester compound can be readily dissolved in the base oil, and readily exhibits the effect corresponding to the content thereof.

For effectively decreasing the coefficient of friction in a sliding portion while taking the stability and the wear resistance of the refrigerator oil in consideration, the content of the polyphosphate ester compound is more preferably from 0.5 to 5.0% by mass, further preferably from 1.0 to 5.0% by mass, and particularly preferably from 1.0 to 3.0% by mass.

[Organic Carboxylic Acid Metal Salt]

The organic carboxylic acid used in the organic carboxylic acid metal salt in the present embodiment has from 6 to 60 carbon atoms. The organic carboxylic acid is preferably an organic carboxylic acid having 6 to 24 carbon atoms, and more preferably an organic carboxylic acid having 16 to 20 carbon atoms.

Examples of the organic carboxylic acid include an aliphatic saturated monocarboxylic acid, an aliphatic unsaturated monocarboxylic acid, an aliphatic dicarboxylic acid, an aromatic carboxylic acid, and an alicyclic carboxylic acid.

More specifically, examples of the aliphatic saturated monocarboxylic acid include a straight-chain fatty acid, such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, cerotic acid, and lacceroic acid; and a branched fatty acid, such as 2-methylpentanoic acid, 2,2-dimethylbutanoic acid, 2-methylhexanoic acid, 5-methylhexanoic acid, 2,2-dimethylheptanoic acid, 2-ethyl-2-methyl-butanoic acid, 2-ethylhexanoic acid, dimethylhexanoic acid, 2-n-propylpentanoic acid, 3,5,5-trimethylhexanoic acid, dimethyloctanoic acid, isotridecanoic acid, isomyristic acid, isostearic acid, isoarachic acid, and isohexanoic acid.

Examples of the aliphatic unsaturated monocarboxylic acid include palmitoleic acid, oleic acid, elaidic acid, linoleic acid, and linolenic acid, and also include an unsaturated hydroxy acid, such as ricinoleic acid. Examples of the aliphatic dicarboxylic acid include adipic acid, azelaic acid, and sebacic acid, and examples of the aromatic carboxylic acid include benzoic acid, phthalic acid, trimellitic acid, and pyromellitic acid. Examples of the alicyclic carboxylic acid include naphthenic acid.

Dimer acids and trimer acids of these fatty acids may also be used.

The organic carboxylic acid may be used solely or as a combination of two or more kinds thereof.

Among these organic carboxylic acids, an aliphatic saturated monocarboxylic acid having 16 to 20 carbon atoms and an aliphatic unsaturated monocarboxylic acid having 16 to 20 carbon atoms are preferred, and among these, an aliphatic unsaturated monocarboxylic acid, such as oleic acid, is more preferred.

Specific examples of the metal constituting the organic carboxylic acid metal salt include an alkali metal, such as lithium, potassium, and sodium, an alkaline earth metal, such as magnesium, calcium, and strontium, and other metals, such as zinc, nickel, and aluminum. The metal is preferably an alkali metal or an alkaline earth metal, more preferably an alkali metal, and particularly preferably potassium. The metal may be used solely or as a combination of two or more kinds thereof.

More preferred specific examples of the organic carboxylic acid metal salt among the above include potassium oleate.

The content of the organic carboxylic acid metal salt in the refrigerator oil is preferably 1 ppm or more in terms of metal concentration based on the total amount (mass) of the refrigerator oil. In the present embodiment, with the content thereof of 1 ppm or more in terms of metal concentration, the coefficient of friction can be decreased while improving the wear resistance by using the aforementioned polyphosphate ester compound together. For appropriately achieving the effect, the content of the organic carboxylic acid metal salt is more preferably from 1 to 20 ppm, further preferably from 1 to 10 ppm, and particularly preferably from 1 to 5 ppm, in terms of metal concentration based on the total amount of the refrigerator oil.

The blending method of the organic carboxylic acid metal salt with the refrigerator oil may be any method, and it is preferred that a solvent having the organic carboxylic acid metal salt dissolved or dispersed therein in advance is blended with the refrigerator oil. The method for providing the solvent having the organic carboxylic acid metal salt dissolved or dispersed therein is not particularly limited, and may be such a manner that an organic carboxylic acid and a metal salt are reacted in a solvent, and the organic carboxylic acid metal salt obtained through reaction in advance may be dissolved or dispersed in a solvent.

The solvent may be one capable of dissolving or dispersing the organic carboxylic acid metal salt, examples of which include various alcohol compounds and various ether compounds. Among these, a polyhydric alcohol, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,4-butylene glycol 2,3-butylene glycol, hexylene glycol, octylene glycol, and glycerin, is preferred, and among these, dipropylene glycol is more preferred. The amount of the solvent used is generally from 5 to 50 times the carboxylic acid metal salt (mass).

[Additional Additive]

The refrigerator oil according to the present embodiment may further contain one kind or two or more kinds selected from an antioxidant, an acid scavenger, an anti-foaming agent, an extreme pressure agent, an oiliness agent, an oxygen scavenger, a metal deactivator, and a rust inhibitor, in addition to the aforementioned polyphosphate ester compound and the aforementioned organic carboxylic acid metal salt. Specifically, the refrigerator oil may be formed of the base oil, the aforementioned polyphosphate ester compound, and the aforementioned organic carboxylic acid metal salt, may be formed of the base oil, the aforementioned polyphosphate ester compound, the aforementioned organic carboxylic acid metal salt, and the aforementioned solvent, may be formed of the base oil, the aforementioned polyphosphate ester compound, the aforementioned organic carboxylic acid metal salt, and an additive other than these components, and may be formed of the aforementioned polyphosphate ester compound, the aforementioned organic carboxylic acid metal salt, the solvent, and an additive other than these components. In this case, the base oil may contain a mineral oil and a synthetic oil other than the aforementioned oxygen-containing organic compound, in addition to the oxygen-containing organic compound, and is preferably formed of the oxygen-containing organic compound.

Among the aforementioned various additives, one kind or two or more kinds of an antioxidant, an acid scavenger, and an anti-foaming agent is preferably contained. The additive other than the aforementioned polyphosphate ester compound and the aforementioned organic carboxylic acid metal salt may be preferably contained in an amount of 15% by mass or less, and more preferably from 0 to 5% by mass based on the total amount of the refrigerator oil.

Examples of the antioxidant include a phenol antioxidant, such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and 2,2′-methylenebis(4-methyl-6-tert-butylphenol), and an amine antioxidant, such as phenyl-α-naphthylamine and N,N′-di-phenyl-p-phenylenediamine, and a phenol antioxidant is preferred. From the standpoints of the effects, the economic efficiency, and the like, the content of the antioxidant is generally from 0.01 to 5% by mass, and preferably from 0.05 to 3% by mass, based on the total amount of the refrigerator oil.

Examples of the acid scavenger include an epoxy compound, such as phenyl glycidyl ether, an alkyl glycidyl ether, an alkylene glycol glycidyl ether, cyclohexene oxide, an α-olefin oxide, and an epoxidized soybean oil. Among these, from the standpoint of the compatibility, phenyl glycidyl ether, an alkyl glycidyl ether, an alkylene glycol glycidyl ether, cyclohexene oxide, and an α-olefin oxide are preferred.

The alkyl group in the alkyl glycidyl ether and the alkylene group in the alkylene glycol glycidyl ether may be each branched, and the number of carbon atoms thereof is generally from 3 to 30, preferably from 4 to 24, and particularly preferably from 6 to 16. As for the α-olefin oxide, one having a total number of carbon atoms of generally from 4 to 50, preferably from 4 to 24, and particularly from 6 to 16 may be used. In the present embodiment, the acid scavenger may be used solely, or may be used as a combination of two or more kinds thereof. The content thereof is generally from 0.005 to 5% by mass, and preferably from 0.05 to 8% by mass, based on the total amount of the refrigerator oil, from the standpoints of the effects and the inhibition of sludge generation.

In the present embodiment, by containing the acid scavenger, the stability of the refrigerator oil can be enhanced.

Examples of the anti-foaming agent include a silicone anti-foaming agent and a fluorinated silicone anti-foaming agent. The content of the anti-foaming agent is generally from 0.005 to 2% by mass, and preferably from 0.01 to 1% by mass, based on the total amount of the refrigerator oil.

Examples of the extreme pressure agent include a phosphorus extreme pressure agent, such as a phosphate ester, an acidic phosphate ester, a phosphite ester, an acidic phosphite ester, and amine salts thereof.

These phosphorus extreme pressure agents each have one phosphorus atom in the molecule thereof, and examples thereof include tricresyl phosphate, trithiophenyl phosphate, tri(nonylphenyl) phosphite, dioleyl hydrogenphosphite, and 2-ethylhexyldiphenyl phosphite.

Examples of the extreme pressure agent other than those mentioned above include a sulfur-based extreme pressure agent, such as sulfurized fats and oils, a sulfurized fatty acid, a sulfurized ester, a sulfurized olefin, a dihydrocarbyl polysulfide, a thiocarbamate compound, a thioterpene compound, and a dialkyl thiodipropionate compound.

The content of the extreme pressure agent is generally from 0.001 to 5% by mass, and particularly preferably from 0.005 to 3% by mass, based on the total amount of the refrigerator oil, from the standpoints of the lubricating properties and the stability.

The extreme pressure agent may be used solely or may be used as a combination of two or more kinds thereof.

Examples of the oiliness agent include an aliphatic saturated or unsaturated monocarboxylic acid, such as stearic acid and oleic acid; a polymerized fatty acid, such as a dimer acid and a hydrogenated dimer acid; a hydroxyfatty acid, such as ricinoleic acid and 12-hydroxystearic acid; an aliphatic saturated or unsaturated monoalcohol, such as lauryl alcohol and oleyl alcohol; an aliphatic saturated or unsaturated monoamine, such as stearylamine and oleylamine; an aliphatic saturated or unsaturated monocarboxylic acid amide, such as lauric acid amide and oleic acid amide; and a partial ester of a polyhydric alcohol, such as glycerin and sorbitol, and an aliphatic saturated or unsaturated monocarboxylic acid.

These compounds may be used solely, or may be used as a combination of two or more kinds thereof. The content thereof is generally selected from a range of from 0.01 to 10% by mass, and preferably a range of from 0.1 to 5% by mass, based on the total amount of the refrigerator oil.

Examples of the oxygen scavenger include a sulfur-containing aromatic compound, such as 4,4′-thiobis(3-methyl-6-t-butylphenol), diphenyl sulfide, dioctyldiphenyl sulfide, a dialkyldiphenylene sulfide, benzothiophene, dibenzothiophene, phenothiazine, benzothiapyrane, thiapyrane, thianthrene, dibenzothiapyrane, and diphenylene disulfide; an aliphatic unsaturated compound, such as various olefins, dienes, and trienes; and a terpene compound having a double bond.

Examples of the metal deactivator include an N—[N,N′-dialkyl(alkyl group having 3 to 12 carbon atoms)aminomethyl]triazole.

Examples of the rust inhibitor include a metal sulfonate, an aliphatic amine compound, an organic phosphite ester, an organic phosphate ester, an organic sulfonic acid metal salt, an organic phosphoric acid metal salt, an alkenyl succinate ester, and a polyhydric alcohol ester.

The refrigerator oil according to the present embodiment may further contain other various known additives in such a range that does not impair the object of the present invention.

[Refrigerant]

The refrigerator oil according to the present embodiment is used in combination with a refrigerant, and specifically is mixed with a refrigerant and used in a refrigerator. In other words, in the present embodiment, the refrigerator oil is used in a refrigerator, in the form of a composition for a refrigerator containing the refrigerator oil and a refrigerant. In the composition for a refrigerator, the amounts of the refrigerant and the refrigerator oil used are generally in a range of from 99/1 to 10/90, and preferably from 95/5 to 30/70, in terms of mass ratio (refrigerant)/(lubricating oil). When the mass ratio is in the range, the refrigeration capability of the refrigerator and the lubrication capability can be made appropriate.

Examples of the refrigerant used include one kind or two or more kinds selected from a fluorinated hydrocarbon and a natural refrigerant, such as carbon dioxide, a hydrocarbon, and ammonia.

<Fluorinated Hydrocarbon>

Examples of the fluorinated hydrocarbon include a saturated fluorinated hydrocarbon compound (saturated HFC) and an unsaturated fluorinated hydrocarbon compound (HFO).

The saturated fluorinated hydrocarbon compound is generally a fluoride of an alkane having 1 to 4 carbon atoms, preferably a fluoride of an alkane having 1 to 3 carbon atoms, and more preferably a fluoride of an alkane having 1 to 2 carbon atoms (methane or ethane). Specific examples of the fluoride of methane or ethane include trifluoromethane (R23), difluoromethane (R32), 1,1-difluoroethane (R152a), 1,1,1-trifluoroethane (R143a), 1,1,2-trifluoroethane (R143), 1,1,1,2-tetrafluoroethane (R134a), 1,1,2,2-tetrafluoroethane (R134), and 1,1,1,2,2-pentafluoroethane (R125). Among those, difluoromethane and 1,1,1,2,2-pentafluoroethane are preferred.

The saturated fluorinated hydrocarbon compound may be used solely, or may be used as a combination of two or more kinds thereof. Examples of the case using two or more kinds of saturated fluorinated hydrocarbon compounds in combination include a mixed refrigerant of two or more kinds of saturated fluorinated hydrocarbon compounds having 1 to 3 carbon atoms; and a mixed refrigerant of two or more kinds of saturated fluorinated hydrocarbon compounds having 1 to 2 carbon atoms.

Specific examples of the mixed refrigerant include a mixture of R32 and R125 (R410A), a mixture of R125, R143a, and R134a (R404A), a mixture of R32, R125, and R134a (e.g., R407A, R407C, and R407E), and a mixture of R125 and R143a (R507A).

Examples of the unsaturated fluorinated hydrocarbon compound include those having a carbon-carbon double bond, such as a fluoride of a linear olefin having 2 to 6 carbon atoms that is straight-chain or branched, and a fluoride of a cyclic olefin having 4 to 6 carbon atoms.

More specifically, examples thereof include an ethylene having 1 to 3 fluorine atoms introduced thereinto, a propene having 1 to 5 fluorine atoms introduced thereinto, a butene having 1 to 7 fluorine atoms introduced thereinto, a pentene having 1 to 9 fluorine atoms introduced thereinto, a hexene having 1 to 11 fluorine atoms introduced thereinto, a cyclobutene having 1 to 5 fluorine atoms introduced thereinto, a cyclopentene having 1 to 7 fluorine atoms introduced thereinto, and a cyclohexene having 1 to 9 fluorine atoms introduced thereinto.

Among those unsaturated fluorinated hydrocarbon compounds, a fluoride of propene is preferred, a propene having 3 to 5 fluorine atoms introduced thereinto is more preferred, and a propene having 4 fluorine atoms introduced thereinto is most preferred. Specific preferred examples thereof include 1,3,3,3-tetrafluoropropene (HFO1234ze) and 2,3,3,3-tetrafluoropropene (HFO1234yf).

The unsaturated fluorinated hydrocarbon compound may be used solely, or may be used as a combination of two or more kinds thereof, or may be used in combination of a refrigerant other than the unsaturated fluorinated hydrocarbon compound. Examples of the case using a combination with a refrigerant other than the unsaturated fluorinated hydrocarbon compound include a mixed refrigerant of a saturated fluorinated hydrocarbon compound and an unsaturated fluorinated hydrocarbon compound. Specific examples of the mixed refrigerant include a mixed refrigerant of R-32, HFO1234ze, and R152a (such as AC5, mixing ratio: 13.23/76.20/9.96).

<Natural Refrigerant>

Examples of the natural refrigerant include carbon dioxide (carbonic acid gas), a hydrocarbon, such as propane, n-butane, isobutane, 2-methylbutane, n-pentane, cyclopentane, isobutane, and n-butane, and ammonia. The natural refrigerant may be used solely or as a combination of two or more kinds thereof, and may be combined with a refrigerant other than the natural refrigerant. Examples of the case using the natural refrigerant in combination with a refrigerant other than the natural refrigerant include mixed refrigerants with a saturated fluorinated hydrocarbon compound, with an unsaturated fluorinated hydrocarbon compound, and with both of them. Specific examples of the mixed refrigerant include a mixed refrigerant of carbon dioxide, HFO1234ze, and R134a (such as AC6, mixing ratio: 5.15/79.02/15.41).

In the present embodiment, among these refrigerants, a fluorinated hydrocarbon is preferred, and a saturated fluorinated hydrocarbon is more preferred. The refrigerant may be a mixture of the saturated fluorinated hydrocarbon and another refrigerant, and is preferably formed only of the saturated fluorinated hydrocarbon. Among them, R32, R125, and R410A, which is a mixture thereof, are further preferred. The refrigerant particularly preferably contains R32, and in this case, the proportion of R32 in the entire refrigerant based on the total amount of the refrigerant is preferably 50% by mass or more, more preferably 70% by mass or more, and most preferably 100% by mass, i.e., a refrigerant containing R32 solely.

[Refrigerator]

The refrigerator oil or composition for a refrigerator according to the present embodiment is used by charging in an interior of a refrigerator. The refrigerator herein has a refrigeration cycle constituted by essential components including a compressor, a condenser, an expansion mechanism (e.g., an expansion valve), and an evaporator, or including a compressor, a condenser, an expansion mechanism, a dryer, and an evaporator. The refrigerator oil is used for lubricating, for example, a sliding portion provided in a compressor.

The sliding portion of a refrigerator is preferably between metals, and examples of the metal in the sliding portion include iron and a steel material. The refrigerator oil of the present embodiment can decrease the coefficient of friction while enhancing the wear resistance between iron or steel materials.

More specifically, the refrigerator oil and the composition for a refrigerator can be used, for example, for various refrigerator systems, hot water systems, and heating systems, such as a car air conditioner, a gas heat pump (GHP), an air conditioner, a refrigeration chamber, an automatic vending machine, a showcase, a hot water supply machine, and a floor heater.

[Production Method of Refrigerator Oil]

A method for producing a refrigerator oil according to one embodiment of the present invention includes blending at least the polyphosphate ester compound and the organic carboxylic acid metal salt with the base oil containing an oxygen-containing organic compound, so as to produce the refrigerator oil. In the method, one kind or two or more kinds of the aforementioned additives may be blended in addition to the polyphosphate ester compound and the organic carboxylic acid metal salt. The detailed descriptions for the base oil, the polyphosphate ester compound, the organic carboxylic acid metal salt, and the additives may be the same as described above, and are omitted herein.

EXAMPLES

The present invention will be described more specifically with reference to examples below, but the present invention is not limited to the examples. The properties of the base oil and the characteristics of the refrigerator oil and the composition for a refrigerator were obtained by the procedures shown below.

(1) Kinetic Viscosity

The kinematic viscosity was measured with a glass capillary viscometer according to JIS K2283:2000.

(2) Lubricating Property Test

The coefficient of friction and the ring wear amount in a sliding portion of each of the compositions for a refrigerator were measured in an R32 (difluoromethane) refrigerant environment using a sealing-type block-on-ring friction tester (LFW-1) under the following conditions.

Ring: FC250

Block: SKH51

Number of revolutions: 1,000 rpm

Preconditioning: Load 300 N×1 minute

Load: 500 N

Time: 30 minutes

Oil temperature: 80° C.

Refrigerant pressure: 0.4 MPa

Examples 1 to 14 and Comparative Examples 1 to 14

Refrigerator oils and compositions for a refrigerator using the refrigerator oils of Examples and Comparative Examples shown in Table 1 were prepared and subjected to the lubricating property test. The results are shown in Table 1.

TABLE 1 Example 1 2 3 4 5 6 7 Base oil PVE 98.25 97.25 96.25 98.25 98.25 98.25 — PAG — — — — — — 98.25 ECP — — — — — — — POE — — — — — — — Additive Polyphosphate ester 1.00 2.00 3.00 — — — 1.00 compound 1 Polyphosphate ester — — — 1.00 — — — compound 2 Polyphosphate ester — — — — 1.00 — — compound 3 Polyphosphate ester — — — — — 1.00 — compound 4 Diluted product of organic 0.05 0.05 0.05 0.06 0.05 0.05 0.05 carboxylic acid metal salt Antioxidant 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Acid scavenger 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Anti-foaming agent 0.10 0.10 0.10 0.10 0.10 0.10 0.10 (Total) 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Metal concentration (ppm) 2 2 2 2 2 2 2 (derived from organic carboxylic acid metal salt) in refrigerator oil Lubricating Coefficient of friction (—) 0.041 0.039 0.034 0.048 0.046 0.047 0.050 property test Ring wear amount (mg) 0.2 0.1 0.1> 0.2 0.2 0.2 0.2 Example 8 9 10 11 12 13 14 Base oil PVE — — — — — — — PAG 96.25 98.25 96.25 96.25 96.25 — — ECP — — — — — 96.25 — POE — — — — — — 96.25 Additive Polyphosphate ester 3.00 — — — — 3.00 3.00 compound 1 Polyphosphate ester — 1.00 3.00 — — — — compound 2 Polyphosphate ester — — — 3.00 — — — compound 3 Polyphosphate ester — — — — 3.00 — — compound 4 Diluted product of organic 0.05 0.05 0.05 0.05 0.05 0.05 0.06 carboxylic acid metal salt Antioxidant 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Acid scavenger 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Anti-foaming agent 0.10 0.10 0.10 0.10 0.10 0.10 0.10 (Total) 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Metal concentration (ppm) 2 2 2 2 2 2 2 (derived from organic carboxylic acid metal salt) in refrigerator oil Lubricating Coefficient of friction (—) 0.048 0.050 0.047 0.046 0.045 0.051 0.050 property test Ring wear amount (mg) 0.1> 0.2 0.1> 0.1> 0.1> 0.1> 0.1> Comparative Example 1 2 3 4 5 6 7 Base oil PVE 99.30 98.30 97.30 96.30 98.30 98.30 98.30 PAG — — — — — — — ECP — — — — — — — POE — — — — — — — Additive Polyphosphate ester — 1.00 2.00 3.00 — — — compound 1 Polyphosphate ester — — — — 1.00 — — compound 2 Polyphosphate ester — — — — — 1.00 — compound 3 Polyphosphate ester — — — — — — 1.00 compound 4 Diluted product of organic — — — — — — — carboxylic acid metal salt Antioxidant 3.30 3.30 3.30 3.30 3.30 3.30 3.30 Acid scavenger 3.30 3.30 3.30 3.30 3.30 3.30 3.30 Anti-foaming agent 0.10 0.10 0.10 0.10 0.10 0.10 0.10 (Total) 100.00 100.00 100.00 100.0 100.00 100.00 100.00 Metal concentration (ppm) 0 0 0 0 0 0 0 (derived from organic carboxylic acid metal salt) in refrigerator oil Lubricating Coefficient of friction (—) 0.073 0.060 0.057 0.053 0.069 0.065 0.062 property test Ring wear amount (mg) 0.4 0.2 0.1 0.1> 0.1> 0.1> 0.1> Comparative Example 8 9 10 11 12 13 14 Base oil PVE 99.25 — — — — — — PAG — 99.30 96.30 — — — — ECP — — — 99.30 96.30 — — POE — — — — — 99.30 96.30 Additive Polyphosphate ester — — 3.00 — 3.00 — 3.00 compound 1 Polyphosphate ester — — — — — — — compound 2 Polyphosphate ester — — — — — — — compound 3 Polyphosphate ester — — — — — — — compound 4 Diluted product of organic 0.05 — — — — — — carboxylic acid metal salt Antioxidant 3.30 3.30 3.30 3.30 3.30 3.30 3.30 Acid scavenger 3.30 3.30 3.30 3.30 3.30 3.30 3.30 Anti-foaming agent 0.10 0.10 0.10 0.10 0.10 0.10 0.10 (Total) 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Metal concentration (ppm) 2 0 0 0 0 0 0 (derived from organic carboxylic acid metal salt) in refrigerator oil Lubricating Coefficient of friction (—) 0.061 0.085 0.066 0.059 0.055 0.053 0.052 property test Ring wear amount (mg) 0.4 0.1> 0.1> 0.5 0.2 0.7 0.5

In Examples and Comparative Examples, the base oils and the additives are as follows.

Base Oils

PVE: Copolymer of ethyl vinyl ether and isobutyl vinyl ether (molar ratio: 9/1, kinetic viscosity at 100° C.: 7.8 mm²/s), in which both ends are represented by the general formula (A-1-i) and the general formula (A-1-ii) respectively, R^(6a) to R^(8a) are hydrogen atoms, R^(11a) to R^(13a) are hydrogen atoms, both r1 and r2 are 0, and R^(10a) and R^(15a) each are an ethyl group or an isobutyl group

PAG: Polyoxypropylene glycol (kinetic viscosity at 100° C.: 9.8 mm²/s)

ECP: Copolymer of polypropylene glycol (PPG) and polyethyl vinyl ether (PEV) (molar ratio of PPG/PEV: 5/5, kinetic viscosity at 100° C.: 11.2 mm²/s)

POE: Pentaerythritol octanoate (C8 acid) nonanoate (C9 acid) ester (molar ratio of C8 acid/C9 acid: 1/1.1, kinetic viscosity at 100° C.: 8.6 mm²/s)

Additives

Polyphosphate ester compound 1: Mixture of compounds represented by the general formula (5), in which n is from 1 to 3

Polyphosphate ester compound 2: Mixture of compounds represented by the general formula (5), in which n is from 1 to 8

Polyphosphate ester compound 3: Compound represented by the general formula (6)

Polyphosphate ester compound 4: Mixture of compounds represented by the general formula (1), in which R¹, R³, R⁵, and R⁷ are hydrogen atoms, R², R⁴, R⁶, and R⁸ each are an alkyl group having 1 to 20 carbon atoms, R⁹ is a divalent hydrocarbon group having 2 to 20 carbon atoms, and n is from 1 to 8

Diluted product of organic carboxylic acid metal salt: Dipropylene glycol diluted product of potassium oleate (dilution degree: 30 times, potassium concentration in diluted product: 4,000 ppm)

Antioxidant: 2,6-di-tert-butyl-4-methylphenol (DBPC)

Acid scavenger: 2-Ethylhexyl glycidyl ether

Anti-foaming agent: Silicone anti-foaming agent

As is apparent from the results of the lubricating property test of Examples 1 to 14, the coefficient of friction in the sliding portion of the refrigerator can be decreased by adding both the polyphosphate ester compound and the organic carboxylic acid metal salt to the refrigerator oil. The wear resistance can also be improved as is apparent from the small ring wear amounts.

As shown by Comparative Examples 1 to 14, on the other hand, in the case where any one or both of the polyphosphate ester compound and the organic carboxylic acid metal salt is not contained in the refrigerator oil, both the wear resistance and the coefficient of friction cannot be improved. 

1: A refrigerator oil, comprising: a base oil comprising an oxygen-containing organic compound; a polyphosphate ester compound; and a metal salt of an organic carboxylic acid having 6 to 60 carbon atoms. 2: The refrigerator oil according to claim 1, wherein a content of the polyphosphate ester compound is from 0.01 to 5.0% by mass based on the total amount of the refrigerator oil. 3: The refrigerator oil according to claim 1, wherein a content of the metal salt of an organic carboxylic acid is 1 ppm or more in terms of metal concentration based on the total amount of the refrigerator oil. 4: The refrigerator oil according to claim 1, wherein the oxygen-containing organic compound is at least one selected from the group consisting of a polyvinyl ether compound, a polyoxyalkylene glycol compound, a copolymer of a poly(oxy)alkylene glycol or a monoether thereof and a polyvinyl ether, and a polyol ester compound. 5: The refrigerator oil according to claim 1, wherein: the polyphosphate ester compound is a compound represented by the following general formula (1):

n represents an integer of from 1 to 10; R¹ to R⁸ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms; and R⁹ represents a divalent hydrocarbon group having 2 to 20 carbon atoms. 6: The refrigerator oil according to claim 5, wherein in the general formula (1) R⁹ comprises an arylene group.
 7. The refrigerator oil according to claim 5, wherein in the general formula (1), R⁹ represents a group represented by the general formula (2) or (3):

8: The refrigerator oil according to claim 1, wherein the polyphosphate ester compound is at least one selected from the group consisting of compounds represented by the following general formulae (5) and (6):

wherein in the formula (5), n represents an integer of from 1 to
 10. 9: The refrigerator oil according to claim 1, wherein the metal salt of an organic carboxylic acid is an alkali metal salt of an organic carboxylic acid. 10: The refrigerator oil according to claim 1, wherein the metal salt of an organic carboxylic acid is a metal salt of an organic carboxylic acid having 16 to 20 carbon atoms. 11: The refrigerator oil according to claim 1, wherein the metal salt of an organic carboxylic acid is potassium oleate. 12: A composition for a refrigerator, the composition comprising a refrigerant and the refrigerator oil according to claim
 1. 13: The composition for a refrigerator according to claim 12, wherein the refrigerant is at least one selected from the group consisting of a fluorinated hydrocarbon, carbon dioxide, a hydrocarbon, and ammonia. 14: A method for producing a refrigerator oil, the method comprising blending at least a polyphosphate ester compound and a metal salt of an organic carboxylic acid having 6 to 60 carbon atoms with a base oil containing an oxygen-containing organic compound to obtain a refrigerator oil. 